Many geographic locations have insufficient rainfall or dry spells that require turf and landscaping to be watered to maintain the proper health of the vegetation. Turf and landscaping are often watered utilizing an automatic irrigation system that includes a programmable controller that turns a plurality of valves ON and OFF to supply water through underground pipes connected to sprinklers. Golf courses, playing fields and other large areas typically require rotor-type sprinklers that eject a long stream of water via a single relatively large nozzle that oscillates through an adjustable arc. Smaller areas are often watered with spray heads or rotary stream sprinklers. Spray heads eject a fan-shaped pattern of water at a relatively high rate and much of this water often flows off the vegetation and/or blows away and is wasted. Rotary stream sprinklers eject relatively small individual streams of water and use less water than spray head sprinklers. In some cases drip nozzles are employed in residential and commercial irrigation systems for watering trees and shrubs, for example.
Rotary stream sprinklers sometimes incorporate a turbine and gear train reduction for slowly rotating the nozzle head or stream deflector. The turbine is typically located at the bottom of the sprinkler, below the gear box that holds the gear train reduction, and above the stator where one is employed. A rotary stream sprinkler can also use the water to directly power the stream deflector, in which case the flutes formed on the underside of the stream deflector that form and channel the streams of water are angled so that a rotational force on the stream deflector is generated. Where the water directly provides the rotary force to the stream deflector, a brake or damper is employed to slow the rate of rotation of the stream deflector.
FIG. 1 illustrates a stream deflector 2 of a conventional rotary stream sprinkler. The inner end of each of the flutes 4 terminates adjacent, and is aligned with, the rotational axis 6 of the stream deflector 2. Rotary stream sprinklers typically include a nozzle plate 8 (FIG. 2) with a suitably shaped orifice 10 that directs water onto the underside of the stream deflector 2 so that the streams only fall onto the desired shape of coverage, e.g. a ninety degree arc in the example shown. In another conventional rotary stream sprinkler the nozzle plate 12 (FIG. 3) has a cylindrical configuration with multiple orifices 14, 16 and 18 that are either open, have varying degrees of restriction, or are plugged. In yet another conventional rotary stream sprinkler 20 (FIG. 4) the nozzle plate 22 has an arcuate orifice 24. Selected amounts of the orifice 24 can be blocked by inserting a plug 26 of suitable size so that the shape of coverage can be adjusted.
The principal drawback of prior rotary stream sprinklers is that they cannot accurately, uniformly and reliably deliver a predetermined very low precipitation rate over a desired shape of coverage. By way of example, a conventional rotary stream sprinkler designed to provide a ninety degree arc of coverage would require an arcuate orifice in the nozzle plate only six thousandths of an inch wide in order to achieve a flow rate of 3.6 gallons per hour at a typical water pressure of between about 20 PSI and 50 PSI. Such a tiny orifice would soon become blocked by grit and/or mineral deposits. Mover, it would be difficult to rotate the stream deflector of a conventional rotary stream sprinkler at such a low flow rate.